Toilet flush tanks have become highly standardized, but have some variation in size and arrangement of parts. Briefly, the tank is provided with an intake pipe and valve, a float ball, an overflow pipe, a large diameter outlet valve and actuating means for opening the outlet valve.
In normal operation, the tank is filled through the intake pipe until the intake valve is closed by action of the float ball. The water level at which this takes place is adjustable simply by bending the long lever rod which carries the float ball. The overflow pipe guards against a leaky intake valve and/or a maladjusted float. When the toilet is to be flushed the outlet valve is opened by the actuating means, allowing a sudden discharge of the water. Various types of outlet valves are currently marketed. The operational requirements are that the valve flap must remain open, e.g., by buoyance, until the water is discharged and then it must close.
In recent years it has become important to limit water usage and in this regard it is sufficient to use a smaller amount of water when only liquids are to be flushed down the toilet than when solids are to be flushed. Various methods have been proposed for providing selectively a full flush and a partial flush, for example in U.S. Pat. Nos. 3,908,203 Jackson and 3,936,889 Wibroe.